First-principles study of MoS2/metal contacts: structure and bonding

We characterize the adsorption of MoS2 on a variety of metal substrates with different reactivities by means of first-principles density functional theory calculations. Including van der Waals interactions in the density functional is essential to capture the bonding between MoS2 and the metal surface. Yet in many cases reasonable equilibrium binding distances and interface potential steps can be obtained with the PBE generalized gradient approximation functional, whereas the local density approximation can lead to an overbinding. Special care is taken to construct commensurable interface structures that have a mismatch between the MoS2 and metal lattices of <1%. MoS2 is chemisorbed on Ti(0001), which leads to a strong perturbation of its (electronic) structure and a pinning of the Fermi level 0.54 eV below the MoS2 conduction band due to interface states. MoS2 is physisorbed on Au(111), where the bonding hardly perturbs the (electronic) structure. The bonding of MoS2 on the other metals studied lies between these two extreme cases, with interface interactions that are somewhat stronger for the late 3d transition metals Co, Ni, Cu and the simple metal Mg than for the late 4d/5d transition metals Pd, Ag, Pt and the simple metal Al. Even a weak interaction, such as in the case of Al, gives interface states, however, with energies inside the MoS2 band gap, which pin the Fermi level below the conduction band.